Optical illusions are tricks played from our perception. We appear to see an object that does not exist or different then it appears. We may see a different shape or we may not even see the shape at all. Other optical illusions can cause the picture to pop in and out causing movement. Our eyes take in the image and send signals to our brain, but brain tends to group objects together and the grouping allows the picture to move shown in the second picture. Optical illusions can cause issues relating to headaches and migraines. The first picture looks like a spiral, but if you look carefully the picture is actually a small circle surrounded by bigger circles. The second picture shows a popping in and out movement when the eyes meet the picture. Staring at the second picture can cause headaches, migraines, and cause your eye muscles to hurt.